1. Field of the Invention
The invention relates to a misprint correction device of a typewriter.
2. Description of the Prior Art
In response to the public desire to have a mistype correction device on a typewriter, misprint erasing ribbons have appeared in market recently which have a half of their width constituting a black inked part and the other half constituting an erasing part coated with white powder of superior adhesibility, (hereinafter this part is referred to as the white part). However, these ribbons have had the disadvantage that the application of the ribbon to correct a misprint requires a rather complicated operation procedure for a typist, and mishandling often leads to further misprints. The procedure typically is as follows:
I. Move the carriage to bring misprinted position to the typing position.
II. Move the ribbon selector to bring the white portion of the ribbon in the service condition.
III. Print the same letter as was mistyped to erase the misprinted letter.
IV. Press the back spacing key to place the erased part in the printing position because typing causes the carriage to shift one letter space.
V. Operate the ribbon selector to make the black inked part return to the printing position.
VI. Type the correct letter to finish the correction.
Because the portion of an erasing ribbon once used cannot be reused, the portion of the ribbon is typically checked before printing, to be certain that it has never been used before. However, most of the conventional typewriters are devised to shift the ribbon only when the machine is operated for typing. Therefore, there is a fear that when an unused portion of a ribbon is seen near to the printing position before printing, that the once used portion would be subjected to the printing position when actually typed. Therefore a certain long range of the unused part is kept reserved at the portion next to typing position, resulting in a very uneconomical increasing of tape consumption.
A misprint corrector of a typewriter to simplify above described procedures was proposed recently which employs a special key solely used for erasing having a flat surface to cover any letters contained in the typewriter, and only by the operation of this type bar is erasure typing performed by an erasing ribbon regardless of the position of the ribbon selector. This is performed without shifting the carriage by use of a disconnecting engagement of the escapement mechanism which otherwise shifts the carriage for a space of a letter, thereby causing carriage not to be shifted.
In this method, however, a mechanism which can more strongly press the erasing type is required. Because of the large printing surface of the correction key requiring larger pressure to erase a misprinted letter, and the use of the same mechanism as with other typing mechanisms, typing becomes difficult, or requires very large effort to bring the type surface and printing paper surface to uniformly meet together. There is also a strong fear that a part of the sides of the neighboring letters may be erased in performing an erasing type for a letter because the erasing type covers very close to adjacent up and down or left and right elongated letters. Further, the problem of requiring a larger portion of the erasing ribbon to be unused still remains.
Prior to explaining the structure of the invention in accordance with an illustrative example shown in the drawings, in order to make easy the understanding of the invention, the structure and operation of the key point of a conventional typewriter already known and related directly to this invention is explained as follows. In FIG. 1, element 2 is a universal ribbon lever pivotally supported to the machine frame 1 on a shaft 1'. A side beam 3, which is installed horizontally to the lever 2, causes lever 4 which is connected to type key to move rotatively in the direction of arrow X.sub.1. Movement of any one of the type keys causes a type lever (not shown in the drawing) to move rotatively to print a letter. The type lever is connected to a lever 4 by a wire rod 5 connected to the edge of the lever 4. The lever 4 contacts side beam 3 and causes the beam 3 to rotate as shown by arrow X.sub.2 around the shaft 1'. The lever 2 is connected to a wire 8 which operates ratchet mechanism 7 which intermittently rotates a ribbon reel 6' of ribbon winder 6, and causes the ribbon reel 6' to rotate intermittently due to rotational movement of the lever 2 as a letter is printed. As a result ribbon 9 is wound up for the length corresponding to one letter width.
In FIG. 1, element 10 is an escapement mechanism which is fixed to a part of the carriage 11 which (see FIG. 10 and FIG. 11) is supported to rotate freely, as shown enlarged in FIG. 4. Escapement wheel 14 is fixed on the shaft of pinion 13 which meshes with rack 12 which is always pulled in the direction of arrow X. Lever 17, an end of which is formed with a holding pawl 15 acts against the escapement wheel 14 and has projected piece 16 at the other end and is pivotly supported to the machine frame by shaft 18. Lever 23, to which shifting pawl 20 is separately installed on arm 19 thereof and having hooking holes 22 for coil spring 21 at the other end, is also pivotally supported by said shaft 18. In opposition to the lever 23, a swing lever 25 having hooking holes 24, which engages with coil spring 21 suspended between it and hooking hole 22, is supported pivotally by pin 26. Projected piece 16 of lever 17 engages with projection 27 of swing lever 25. Lever 23 is pulled towards swing lever 25 by coil spring 28. Lever 17 is pulled by coil spring 29 to cause the holding pawl 15 to always tend to go in between the teeth of lever 23.
The escapement mechanism 10 is further equipped with an operation mechanism 31 which pivotly supports swing board 32 by a pair of brackets 32.sub.1 and 32.sub.2 fixed to the machine frame about axis 330 as shown enlarged in FIG. 5. An adjustable screw lever 33 is screw attached to the free end of swing board 32, and the top of said screw lever 33 is made to contact to the under face of the arm 19 of lever 23 of the escapement mechanism 10. Against the other free end 34 of swing board 32, pressing lever 35 which presses free end 34 of said swing board 32 of said operation mechanism 31 when a user is pressing any type key or spacing key is installed as shown in FIG. 6. Therefore, pressing any type key or spacing key causes pressing lever 35 to move in the direction of arrow-Y, which presses the free end 34 of swing board 32 of operation device 31 of escapement mechanism 10 to rotate swing board 32 in the direction of arrow-Z. This makes adjusting screw lever 33 rotate arm 19 of lever 23 of escapement mechanism 10 in a counterclockwise direction in FIG. 4, which rotates lever 17, via projection 27 of swing lever 25, which in turn moves with said lever 23 as one body in a counterclockwise direction. Holding pawl 15 then disengages from the escapement wheel while shifting pawl 20 meshes with the escapement wheel which causes escapement mechanism 10 to move carriage or platen 11 for one letter space. The swing plate 32 will be returned to the original position by return spring 28. Backspacing key 36 is shown in FIG. 1.